The new requirements are due to a bill authored by former state Sen. Joe Simitian, a Democrat from Palo Alto.
One of his constituents, Amy Colton of Santa Cruz, suggested the measure after annual mammograms did not reveal her breast cancer until it had reached an advanced stage.
Health officials say nearly half of women over age forty have dense tissue, which can make it more difficult to detect cancer.
Patients with dense breast tissue will also be told their doctors can recommend more mammogram options.
The additional screening information will give women the chance to talk to their doctors about potential risks.
The Associated Press contributed to this report.